1. Field of the Invention
This invention relates generally to a focal plane shutter construction in a single lens reflex camera, and more particularly, it is concerned with a leak-proof device for intercepting harmful light liable to intrude into a film accommodating part of the camera through clearances existing in the moving part of the shutter.
2. Description of the Prior Art
In order to permit the focal plane shutter in a single lens reflex camera to operate, clearances for its movement are provided between the camera body and the shutter curtain. When the camera is used in a bright area, particularly when lens interchanging is done under sunlight, oblique light rays entering into the lens are irregularly reflected at the plane within the light-transmitting frame of the camera body, and such reflected light rays may pass through the abovementioned clearances to create fogging on the film surface, even if the shutter is in its closed position.
This difficulty has been recognized in the art, and efforts have been made to overcome same. Thus, there has been adopted a technique of intercepting the harmful light tending to pass through the clearances by providing within such clearances a light-leakage preventive device having a light-intercepting member attached thereto. More specifically, according to known techniques, the harmful light has been intercepted either by (1) attaching velveteen to the camera body within the clearances or to the outer surface of the mirror box to cause the upright short pile of the velveteen to contact the shutter curtain, or (2) by attaching one side edge of a rubber-coated cloth curtain such as a laminate of silk cloth and rubber material like buyl rubber, nitrile rubber, etc. to the camera body or the outer surface of the mirror box, and causing the other side edge of the rubber-coated cloth curtain to contact the shutter curtain.
However, the abovementioned first case, in which the velveteen is employed, has a defect such that if an attempt is made to improve the light-intercepting characteristics of the shutter, increase in the contact area and contact pressure between the velveteen and the shutter curtain would occur with the consequent reduction or irregularity in the speed of movement of the shutter curtain.
To reduce such contact area and pressure between the velveteen and the shutter curtain, the side edge of the rubber-coated cloth curtain may be linearly contacted with the surface of the shutter curtain to effect the light-interception. However, such rubber-coated cloth curtain having a silk base available at present has not sufficient strength to withstand friction or abrasion during the take-up or movement of the shutter curtain, and is liable to fray, wherefor it is not sufficiently durable for practical use.
To compensate for this defect, the rubber-coated curtain has been made in the form of a pocket or a deformed cylinder with its protuberant surface, not its side edge, contacting the shutter curtain. However, even this method is disadvantageous in that not only the contact area and contact pressure between the rubber-coated cloth curtain and the shutter curtain increases, but also the state of contact therebetween becomes unstable and non-uniform.